The pathophysiological mechanisms of Central Nervous System (CNS) disease in Systemic Lupus Erythematosus (SLE) will be studied in this proposal. Antineuronal antibodies in the serum of CNS-SLE Patients are a central feature of the disease, however their specific target antigens have not been well characterized. I have recently identified, initially characterized and partially isolated a 50 kD neuronal cell surface protein as a specific target antigen of antineuronal antibodies in CNS-SLE patients. Thus, the goal of this proposal is to elucidate the primary structure of the 50 kD antigen and to delineate the possible pathogenic role of the anti-50 kD autoantibodies. The experimental approach is to use a combination of molecular, biochemical and immunological techniques to define the target antigen. The primary structure of the 50 kD neuronal antigen will be determined via cDNA cloning after final purification of the protein by conventional and immunoaffinity chromatography. A panel of monoclonal antibodies will be generated to probe the 50 kD protein and to probe the functional epitopes. Dominant autoreactive epitopes will be determined with affinity purified human antisera from CNS-SLE patients as well as monoclonal antibodies. The brain localization and intracellular distribution of the 50 kD protein will be studied by immunocytochemistry and immunoblot analysis of subcellular fractions to help elucidate the functional significance of the antigen and to provide clues as to the possible cellular and molecular mechanisms of brain injury CNS-SLE. The pathological effects of the anti-50 kD antibody on cultured neuronal cells with respect to cell toxicity and neurotransmitter release will also be studied. Overall the results obtained will provide data on the cellular and molecular events in the brain that prevail in SLE patients with neurological disfunction.